1. Field of the Invention
This invention relates to a head flange mounting device for a turbo-machine, such as a centrifugal compressor, which provides an improved construction for mounting a head flange on the inner circumferential surface of a casing by means of a shear key.
2. Description of the Prior Art
As a turbo-machine starts its operation, the casing expands radially due to a rise in the temperature of the fluid handled and the internal pressure of the casing. With an increase in the temperature of the fluid handled, the head flange also expands radially, but the temperature in the central portion of the turbo-machine shows no appreciable rise. Combined with the structural relation between the casing and the flange, this renders the expansion of the head flange less in amount than that of the casing. In addition, the head flange is not restrained radially because it is mounted on the casing by means of a shear key. As a result, a clearance between the head flange and the casing grows larger in size with time after the startup of the machine, so that misalignment of the head flange and the casing might occur. This might bring about a misalignment of a labyrinth seal provided to the casing and a rotary shaft supported by the casing. There are possibilities that the labyrinth seal and the rotary shaft might be accidentally brought into contact with each other. In order to avoid such possibilities, the present practice in the turbo-machine manufacturing industry is to increase the clearance between the labyringth seal and the rotary shaft in design by taking into consideration the misalignment of the two parts that might occur during operation. Because of this, the head flange of a turbo-machine of the prior art has suffered the disadvantage that no satisfactory seal is provided.
To avoid a reduction in the effect achieved by sealing requires keeping the center axis of the head flange in alignment with the center axis of the casing at all times. Various proposals have hitherto been made to provide head flange mounting devices capable of mounting the head flange on the casing by fulfilling the aforesaid requirement. Some of these proposals will now be outlined, to enable the invention to be better understood.
In one head flange mounting device known in the art, the head flange mounted at its outer circumferential surface on the inner circumferential surface of an end portion of the casing by means of a shear key is forced against the casing by a plurality of fixed bolts extending through the casing in several circumferentially spaced positions, to avoid relative movements of the head flange and casing radially thereof. In this type of device, it is necessary that the operator tighten the fixed bolts to avoid displacement of the head flange from the casing as the clearance between the head flange and the casing increases in size with time following the initiation of an operation. A drop in the temperature of the head flange and the casing caused by interruption of the operation reduces the clearance between the head flange and the casing and requires loosening of the fixed bolts to avoid damage to the latter that have been tightened. This tightening and loosening of the fixed bolts is time consuming and causes a lot of trouble. Moreover, the arrangement whereby the head flange is forced against the casing by the fixed bolts makes it difficult to keep the head flange and the casing in alignment with each other at all times.
Another head flange mounting device of the prior art employs a plate instead of the fixed bolts of the first example which plate is attached to an end face of the casing to pull the head flange through check bolts, to thereby keep the head flange from moving in the radial direction. More specifically, frictional forces are generated on the surfaces of the casing and the shear key and the head flange and the shear key in contact with each other by the clamping forces of the check bolts, so that the relative movements of the head flange and the casing radially thereof can be prevented by the frictional forces generated in this way. The second example of the prior at suffers the disadvantage that the force tending to restrain the radial movements of the head flange and the casing is not high enough to achieve the desired result, the restraining force being influenced by the clamping force exerted by the check bolts and the coarseness of the contacting surfaces of the parts. The device of this example is not capable of keeping the center axis of the head flange in alignment with the center axis of the casing at all times, and the two parts tend to displace from each other due to vibration or thermal expansion during operation.